Grout calculator

Q: How much grout do I need for 100 square feet of 12x12 tile?

**About 6.3 lb of grout, or 7.2 lb with a waste allowance** — one 10 lb box — for 3/8 in thick tile with a 1/8 in joint. LATICRETE publishes 128 sq ft per 8 lb bag for exactly that tile and joint, which is the same 6.25 lb per 100 sq ft. If the tile is 1/4 in thick it drops to 4.2 lb, and if it is 1/2 in it climbs to 8.3 lb.

Enter the area, the tile size and the joint width, and this returns pounds of grout and the bags to buy. The input that matters most is tile thickness: it is the depth of every joint, so a 1/2 in tile takes twice the grout of a 1/4 in tile on the same floor.

Area to grout The tiled surface, floor or wall. Grout scales with area, so a backsplash and a floor use the same maths. Tile width Small tile means more joint per square foot. A 2 in mosaic needs roughly four times the grout of a 12 in tile. Tile length Tile thickness This is the joint depth. Wall tile is often 1/4 in, floor porcelain 3/8 in, and porcelain pavers 1/2 in or more. Measure the edge of a tile. Grout joint width Use the spacer size you are actually setting with. 1/8 in and narrower is unsanded territory; 1/8 in and wider takes sanded grout. Extra for waste % Grout waste is high: what stays in the bucket, what gets stiff before you reach it, and the batch you throw away after a colour test. Grout type Lightweight grouts replace some sand with recycled glass, so a smaller box fills the same joints. Bag or box size

Grout needed 7.2 lb

Bags or boxes to buy 1 bags Rounded up. Grout is cheap and colour lots vary — buy the spare now.

Per 100 sq ft of this tile 7.2 lb

One bag covers 400 sq ft Before waste, so you can check this against the coverage chart on the bag.

How the number is worked out

The joints are a grid of channels. Each channel has a cross-section of joint width × joint depth, and the joint depth is the thickness of the tile. So the volume of grout in one square foot of floor is the length of joint in that square foot multiplied by width and by depth.

For one tile the repeating module is the tile plus one joint in each direction, and the grout in that module is the module area minus the tile area, times the depth. Multiply by the number of modules in a square foot and you have the volume. Converting that volume to pounds needs one more figure, and it is the one figure on this page that nobody publishes: the weight of mixed grout sitting in a joint. This calculator uses 97.5 lb per cubic foot, which is our own fitted value — solved backwards out of LATICRETE's coverage table rather than quoted from anyone's data sheet. It is not a manufacturer's number, and where your own product's sheet gives a coverage for your tile and joint, that sheet wins. How the fit was done, and how far it can be trusted, is set out at the end of this page.

Why this page asks for tile thickness

Tile thickness is the depth of the channel you are filling, so an estimate built from tile size and joint width alone is missing one of the three dimensions of the joint. Same 100 sq ft floor, same 12 × 12 tile, same 1/8 in joint:

1/4 in thick wall tile — 4.2 lb
3/8 in thick floor porcelain — 6.3 lb
1/2 in thick porcelain paver — 8.3 lb

That is a factor of two, decided entirely by a dimension that an area-times-joint-width sum never sees. It is why the field is on this page.

Checked against a published chart

LATICRETE PERMACOLOR Grout, Data Sheet DS-250 prints an approximate coverage table in square feet per 8 lb bag, by tile size including thickness and by joint width. The geometry above reproduces it: 12 × 12 × 3/8 tile at a 1/8 in joint gives 128 sq ft per 8 lb bag against a published 128; a 2 × 2 × 1/4 mosaic gives 34 against a published 34; 12 × 24 × 3/8 gives 170 against 170. Across all 23 tile sizes and three joint widths in that table the formula stays within 2%.

If your grout came with its own chart, use the chart — this calculator exists for the tile sizes and thicknesses no chart lists.

Sanded or unsanded, and why the answer is a width

The dividing line is the joint, not the tile. CUSTOM Building Products publishes joint widths 1/8 in to 1/2 in for Polyblend Sanded Grout (TDS-129) and up to 1/8 in for Polyblend Non-Sanded Grout (TDS-130). Below 1/8 in the sand will not pack into the joint; above it, unsanded grout shrinks and cracks.

At exactly 1/8 in either works, and then the tile decides: sand can scratch polished marble, glass and metal tile, so those get unsanded or a manufacturer-approved alternative.

Lightweight grout is not the same weight per joint

A 17 lb box of CUSTOM's Prism "covers the same area as a typical 25 lb bag of conventional grout" (TDS-128), because the sand is partly replaced with recycled glass. Do not convert one to the other by weight — switch the grout type above and the calculator uses the lighter density.

Waste, and mixing what you can actually use

No manufacturer publishes a waste percentage for grout, so the 15% here is trade practice rather than a citable figure. It covers the grout left in the bucket, the stiff batch you discard, and the sample you mix to check the colour.

Mix only what you can place inside the pot life — 1–2 hours for Polyblend Sanded (TDS-129), 60–90 minutes for the fast-setting Prism (TDS-128). Both sheets say to let the mix slake for 10 minutes and then remix, and neither lets you add water later to loosen it: that is what causes patchy colour and pinholes.

The density is fitted, and the grid is an assumption

The 97.5 figure is a fitted value, not a published one. No grout maker prints the weight of its mixed product sitting in a joint. What the section above describes is an inversion: LATICRETE's chart was taken as given and the density that regenerates it was solved for. The agreement is close enough to be good evidence that the chart and this page are doing the same geometry, but it is still one manufacturer's product standing in for every cement grout, and another maker's mix need not weigh the same. The lightweight density is one step further out again — it is that same fitted figure scaled by CUSTOM's statement about how far a box of Prism goes. Both options here are cement-based; epoxy is a different material with its own yield and is not on this page at all.

The shape model is a rectangular grid with one joint width. It multiplies out a repeating module of tile plus joint, which is what a square or a subway layout is, and is not what a hexagon, a penny round, a pebble sheet or a deliberately irregular mosaic is. Those have no single width to type in. The page also holds one tile at a time: a floor with a border or an inset, or a shower whose walls and pan are different products, has to be run once for each and the answers added.

Finally, the joint is modelled as completely full — flush at the top and running the whole thickness of the tile. Where thin-set has squeezed up between the tiles the channel is shallower than that and you will use less than the answer says. Nothing here can see it, which is part of why the waste allowance sits as high as it does.

Common cases

Questions people ask

How much grout do I need for 100 square feet of 12x12 tile?

About 6.3 lb of grout, or 7.2 lb with a waste allowance — one 10 lb box — for 3/8 in thick tile with a 1/8 in joint. LATICRETE publishes 128 sq ft per 8 lb bag for exactly that tile and joint, which is the same 6.25 lb per 100 sq ft. If the tile is 1/4 in thick it drops to 4.2 lb, and if it is 1/2 in it climbs to 8.3 lb.

Does tile thickness change how much grout I need?

Yes, proportionally. The joint depth is the tile thickness, so going from 1/4 in to 1/2 in tile doubles the grout on an identical floor. Leave thickness out of the sum — multiply area by joint width and stop — and the answer can be half of what you need, which is why this calculator asks for it.

Should I use sanded or unsanded grout?

Go by joint width. CUSTOM Building Products lists sanded grout for 1/8 in to 1/2 in joints and non-sanded for joints up to 1/8 in. Narrower than 1/8 in, sand will not pack into the joint; wider than 1/8 in, unsanded grout shrinks and cracks. At exactly 1/8 in the tile decides — use unsanded on polished marble, glass or metal, which sand can scratch.

How much grout for a mosaic backsplash?

Far more than for a floor. A 2 × 2 in mosaic 1/4 in thick with 1/8 in joints takes 23 lb per 100 sq ft, about four times what 12 × 12 floor tile takes, because there is four times as much joint per square foot. A typical 30 sq ft backsplash still only needs one 8 lb bag, but a whole shower in 1 in mosaic can take 25 lb.

How many bags of grout for a shower?

Measure the tiled area rather than the shower size — walls, floor and curb are all separate faces. A 3 × 5 ft shower tiled to 7 ft is roughly 130 sq ft of wall plus 15 sq ft of floor. In 3 × 6 in subway at 1/16 in joints that is about 10 lb, but the small mosaic floor alone can add as much again.

Can I keep grout and use it next week?

The dry powder keeps if the bag stays sealed and dry, but mixed grout does not. Pot life is 1–2 hours for standard sanded grout and 60–90 minutes for fast-setting types, and adding water to soften a stiffening batch causes colour variation, pinholes and shrinkage cracks. Mix in small batches instead.

Last reviewed 2026-07-31